1. Field of the Invention
This invention relates to the disproportionation of isoparaffins. In another aspect, the invention concerns a process of disproportionating isopentane with a catalyst composition comprising an aluminum halide on a support.
2. Description of the Prior Art
As gasoline and other motor fuels become increasingly regulated, petroleum refiners must alter current gasoline blending techniques in order to comply with stricter federal and state standards regarding certain product characteristics such as, for example, sulfur content, aromatics content, and Reid vapor pressure (RVP). Stricter RVP limits pose a problem for refiners, who produce substantial volumes of relatively volatile, high vapor pressure hydrocarbons such as isopentane (RVP of 21 psi), which have traditionally been blended into gasoline and other motor fuels. However, these stricter limits coupled with the emergence of new, relatively high RVP gasoline additives that provide a substantial RVP boost upon blending (e.g., ethanol), have greatly reduced the amount of isopentane and other volatile components that can be successfully blended into the finished products. However, as refinery production rates continue to increase to meet increased demand, a process of economically utilizing excess isopentane and other high RVP components is desirable. Currently, the proposed solutions include the seasonal storage and blending of isopentane and other high RVP components, the production of lower grade blendstocks, and/or the sale of finished products to less regulated markets. Overall, these solutions do not adequately address the problem because they fail to consistently account for the entire volume of excess isopentane, are cost intensive, and, ultimately, result in reduced profitability. Thus, an economic means of managing excess isopentane inventory is desirable.
One proposed process of economically reducing excess isopentane inventories is to disproportionate isopentane into hexane (C6) and butane (C4) isomers, such as, for example, isohexanes (iC6) and isobutane (iC4). As used herein, the term “isohexanes” refers to dimethylbutane isomers, methylpentane isomers, and mixtures thereof. Isohexanes, which have substantially lower RVP values, can be more easily blended into motor fuels. Isobutane is a primary feedstock for the alkylation process, which converts low molecular weight olefins (i.e., propylene and butylenes) into low vapor pressure, high octane blendstocks such as isooctane. Thus, an improved process for disproportionating isopentane would be a significant contribution to the art.